The present invention relates in general to an attachment lug adapted to be fixed to an end region of a cylindrical body or member such as a power cylinder so that loads directed on the attachment lug are transmitted to the cylindrical body, and to an assembly of the attachment lug connected to the cylindrical body.
In particular, the invention relates to an attachment lug adapted to be fixed on the end region of a cylindrical body or member which is suitable for use as a fork structure in the landing gear of aircraft. Such apparatus cperate under high stresses and rigorous conditions and for this reason must possess good strength characteristics. Additionally, the apparatus must be lightweight. In the following description, the invention is described in connection with its application to aircraft landing gear wherein both of the characteristics mentioned above are required.
Generally, the landing gear of an aircraft enables the aircraft to operate on the ground. The landing gear is therefore subjected to extremely high stress conditions. The landing gear performs four functions and therefore must be designed with these functions in mind. In particular, firstly, the landing gear must serve as a static support for the aircraft when the aircraft is on the ground. Secondly, the landing gear enables the aircraft to taxi on the ground during take-off and landing. Thirdly, the landing gear must be capable of absorbing the vertical kinetic energy of the aircraft during landing. Finally, the landing gear must operate as a suspension and shock damping element in order to absorb impact forces which are directed on it as the aircraft moves over the ground due to bumps and other discontinuities in the ground. The landing gear of an aircraft generally comprises in its entirety wheels, brakes, a shock absorber unit and the necessary structural components by which these elements are joined to the structure of the aircraft.
The shock absorbing function of most conventional aircraft landing gears is performed by a component which operates in accordance with the oleo-pneumatic principle. Such landing gears are considered to absorb vertical energy most efficiently for a given weight and size. In such landing gears, the shock absorbing component comprises a piston-cylinder combination which is partially filled with hydraulic fluid and partially with air or nitrogen gas. The piston and cylinder are adapted to move with respect to each other, usually by means of slide bearings. During landing of the aircraft, the vertical energy is absorbed as the piston, while sliding inwardly into the cylinder, forces the hydraulic fluid to flow through an orifice from one chamber in the cylinder to another. In certain landing gears of this type the flow through the orifice is controlled by means of a metering pin.
The piston-cylinder component of the landing gear usually functions not only as a shock absorbing component but also as a structural component of the landing gear. Other structural components of the landing gear include the fork, the trunnion, and torque links that prevent the wheel from freely castering. The trunnion is connected to the main aircraft structure by pivot pins or the like. In other types of landing gears, a separate component connected to the piston-cylinder or to the trunnion functions as the main structural component. In certain aircraft using this type of landing gear, this separate component comprises an actuator which is part of the landing gear retracting mechanism.
The components of conventional oleo-pneumatic landing gears are generally formed of metallic material. The fork, piston, cylinder and trunnion are usually made of steel while the torque links are usually made of aluminum or steel. A significant drawback of such metallic construction is the weight of the landing gear which reduces the load capacity of the aircraft. Of course, it is desireable to maximize the load-carrying capacity of an aircraft from an economic viewpoint.
Although conventional landing gears have the general construction described above, the landing gear of one type of aircraft will generally differ in detailed construction from the landing gear of another aircraft, mainly due to the restricted space within which the landing gear must be provided and due to the location of the points at which the landing gear is connected to the aircraft structure. In many types of landing gears, the cylinder and the trunnion including the lugs are manufactured from a single forging. Depending on the particular design, the fork of the landing gear is either a full fork or a semi-fork. In some types of landing gears, the wheels, tires and brakes are situated on one side of the vertical axis of the landing gear in which case no fork is required at all.